Workflow equation in system with rework

Use this forum to post Vensim related questions.
Post Reply
nesfehani
Junior Member
Posts: 2
Joined: Fri Oct 13, 2017 11:21 am
Vensim version: PLE

Workflow equation in system with rework

Post by nesfehani »

Hello,

I'm a beginner at modeling with Vensim and my question is about a fundamental concept. Attached you can find two images from Vensim help regarding the rework and errors. I have problem with workflow equation and do not know according to what equation my workflow graph can have the peaks after reaching zero. Your suggestion is highly appreciated.
Attachments
2.jpg
2.jpg (35.06 KiB) Viewed 2988 times
1.jpg
1.jpg (33.63 KiB) Viewed 2988 times
Administrator
Super Administrator
Posts: 4573
Joined: Wed Mar 05, 2003 3:10 am

Re: Workflow equation in system with rework

Post by Administrator »

I don't understand what you are asking. Can you upload your model and try and explain what you need?
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391

Units are important!
http://www.bbc.co.uk/news/magazine-27509559
ali
Junior Member
Posts: 2
Joined: Fri Oct 13, 2017 8:17 am
Vensim version: PLE

Re: Workflow equation in system with rework

Post by ali »

please find attached the rework model, and its outcome graphs. I tried to repeat the rework model sample which is in the vensim help, and then compare the outcome of my model with the rework sample. However, as you can see, graphs of my model (work flow and work remaining graph is not the same as vensim sample). I think that my equation for work flow rate is not correct. Could you please let me know how I can fix it?
Attachments
this work flow graph is not the same as the sample
this work flow graph is not the same as the sample
work flow graph.jpg (61.22 KiB) Viewed 2973 times
rework model1.mdl
(3.07 KiB) Downloaded 159 times
the value of work remaining is negative after month 9, which shouldn't be correct
the value of work remaining is negative after month 9, which shouldn't be correct
equations&outputs.jpg (116.92 KiB) Viewed 2973 times
Administrator
Super Administrator
Posts: 4573
Joined: Wed Mar 05, 2003 3:10 am

Re: Workflow equation in system with rework

Post by Administrator »

ali wrote:Could you please let me know how I can fix it?
Is your equation different to the one in the Vensim sample model? You need to go through your work and check everything is identical to the Vensim model.
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391

Units are important!
http://www.bbc.co.uk/news/magazine-27509559
ali
Junior Member
Posts: 2
Joined: Fri Oct 13, 2017 8:17 am
Vensim version: PLE

Re: Workflow equation in system with rework

Post by ali »

the vensim sample doesn't mention the "work flow" equation. so, I'm not sure my equation is correct or not, could you please let me know the correct equation for "work flow" variable in the vensim sample?
Administrator
Super Administrator
Posts: 4573
Joined: Wed Mar 05, 2003 3:10 am

Re: Workflow equation in system with rework

Post by Administrator »

The model can be downloaded from
http://www.vensim.com/documentation/ind ... ?21495.htm

You will also find it on your hard drive under C:\Users\Public\Vensim\Help\Models\ModelGuide\3PROJ
Advice to posters seeking help (it really helps us to help you)
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391

Units are important!
http://www.bbc.co.uk/news/magazine-27509559
tomfid
Administrator
Posts: 3806
Joined: Wed May 24, 2006 4:54 am

Re: Workflow equation in system with rework

Post by tomfid »

I haven't looked at it for a while, but the model in the Help system contains what I consider to be a fairly basic error, which is also in your sample above.

The workflow equation is not constrained such that the workflow is less than or equal to the available work, so Work Remaining goes negative.

In the final Help system model, it's:

Code: Select all

work flow = IF THEN ELSE(project is done,0,Veteran Workforce*productivity)
and your equation is:

Code: Select all

work flow = 150*IF THEN ELSE(work remaining>0,1,0)
In both cases, this should be amended to something like:

Code: Select all

work flow = IF THEN ELSE(project is done,0,MIN(Veteran Workforce*productivity,Work Remaining/TIME STEP))
The MIN( ... , Work Remaining/TIME STEP) ensures that Work Remaining remains nonnegative.
Post Reply